In prior art lighting devices, a reflector placed in a spaced relationship behind a light source for reflecting light rays emanating from the light source was either a suitably shaped reflective mirror facing in a given direction in which the area to be illuminated is located, or a reflective mirror with a particular geometrical shape. The former reflective mirror aimed primarily at reflecting, in a desired direction, light rays emanating from the light source toward the mirror, to utilize the light efficiently, and no emphasis was placed on geometrical control of reflected light rays. On the other hand, the latter reflector was typically either a parabolic reflector having a surface of revolution of a parabola or an elliptic reflector with a surface of revolution of an ellipse. As is well known, light rays which emanate from a point light source at the focus of a parabolic reflector are collimated or made parallel, after they are reflected by the reflector. Also known is a fact that light rays emanating from a point light source at one of the focuses of an elliptic reflector converge at the other focus of the ellipse and simply radiate therefrom. Thus both of them were limited to particular uses and functions.
The prior art reflectors therefore have limitations in that although they were capable of either collimating or diverging light rays after they are reflected by virtue of their geometrical shape, they were not capable of commanding free and complete control over reflected light rays and distributions of luminous fluxes.
Meanwhile, as will be described later, it is known that when light is emitted from a point light source to a reflecting surface behind it, a solid angle corresponding to a given plane angle differs significantly depending upon the angular location of the reflecting surface with respect to the light source. The design of a light reflector of a conventional lighting device was carried out within the framework of the above-noted known principle.
The present invention was made in view of the afore-said practices and limitations, and the object of the invention is to provide an improved or novel illuminating or lighting device having a new and useful reflector structure capable of freely controlling both the direction of light rays and the density of luminous fluxes, and further capable of obtaining desired luminous flux distribution at any area to be lighted in connection with, and in consideration of the light distribution characteristics of the light source.